In recent years, demand for fuel-efficient vehicles has increased, and with the increase thereof, rubber compositions for tires providing excellent fuel efficiency are desired. It is known that, in order to improve fuel efficiency, styrene-butadiene rubber or butadiene rubber is modified to promote dispersion of filler. For example, rubbers having a terminal modified with a nitrogen functional group-containing alkoxysilane are suggested as modified rubbers for silica formulation, and terminal-modified butadiene rubbers which are coupled with tin are, suggested as modified rubbers for carbon black formulation. In addition, mercapto group-containing silane coupling agents disclosed in Patent Literature 1 are known to have high reactivity with silica and promote dispersion of silica.
All the above techniques for improving fuel efficiency are effective for styrene-butadiene rubber or butadiene rubber, but are not sufficiently effective for isoprene-based rubbers such as natural rubber, highly purified natural rubber, isoprene rubber, and epoxidized natural rubber.
Rubber compositions for tires generally include isoprene-based rubbers in addition to styrene-butadiene rubber or butadiene rubber. In particular, rubber compositions used for heavy-load tires, which need to have high rubber strength, include isoprene-based rubbers as a main component. Therefore, there is a need for a technique for improving fuel efficiency which is effective for isoprene-based rubbers.